Leukomoid reaction criteria
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leukemoid reaction
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leukemoid reaction definition leukocyte count criteria differentiate CML
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Leukemoid reaction is an exaggerated reactive leukocytosis, usually neutrophilic, that mimics leukemia but is not a myeloproliferative neoplasm.
Diagnostic criteria / typical findings
- Total leukocyte count ≥50 × 10⁹/L (≥50,000/µL), classically with a left shift.
Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 734. - Predominantly mature neutrophils with increased bands, metamyelocytes, and myelocytes.
- Reactive neutrophil changes: toxic granulation, Döhle bodies, and cytoplasmic vacuolation may be present.
- A demonstrable underlying reactive cause, such as severe bacterial infection or sepsis, major inflammation/tissue necrosis, severe hemorrhage or hemolysis, drugs (for example corticosteroids or G-CSF), or cytokine-producing malignancy.
- The count improves when the underlying cause is treated.
Important distinction from CML
| Feature | Leukemoid reaction | Chronic myeloid leukemia |
|---|---|---|
| Cause | Reactive | Clonal myeloproliferative neoplasm |
| Neutrophil alkaline phosphatase (NAP/LAP) | Normal or increased | Low |
| Toxic granulation/Döhle bodies | Often present | Usually absent |
| Basophilia/eosinophilia | Usually absent or mild | Often prominent |
| Platelets and other lineages | Usually no panmyelosis | May show panmyelosis |
| BCR::ABL1 | Negative | Positive |
A peripheral smear alone can be insufficient to exclude CML. If the cause is not clear or leukocytosis persists, obtain BCR::ABL1 testing and consider hematology review. The textbook notes that NAP is normal or elevated in granulocytic leukemoid reactions but decreased in CML. Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 734.
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